This invention relates generally to tube fittings, and more particularly concerns fittings for beaded plastic tubing joints where the plastic material is flexible, and consists for example of polybutylene.
Tubing made of polybutylene has many desirable characteristics among which are: very high strength from cold up to about 180.degree. F., and extremely high stress crack resistance and weather resistance, while remaining very flexible. Further, elongation characteristics are so high that water can freeze in pipe made of this material, with no damage to the pipe. Also, life expectancy of the material is very high. Such pipe and tubing is usable in many areas where copper tubing has been used, and at a fraction of the cost of the latter.
In certain applications, namely where high fluid pressure is encountered, it was found that adequate clamping of the tubing was required. For example, the tubing ends were typically forced over annular serrations on pipe nipples, and external clamping members were employed over the tubing ends. This requires extra work and can result in undersirable flow restrictions associated with the nipples that fit into the tubing ends. Attempts have been made to use external barbed fittings; however, polybutylene is so flexible and crack resistant that the barb would often not bite into the polybutylene, resulting in the tube blowing out of the fitting, under pressure. It was found that the polybutylene could be end-flared in a manner similar to flaring of copper tubing, and that standard brass fittings normally used with copper tubing would work quite well with the polybutylene flared ends; however, such fittings are expensive, the flaring step is time consuming, the material has to be "worked" considerably to produce the flare due to its stretch resistance, and the tube end has to be cut squarely for proper sealing with the fitting.